During the immune response, foreign antigens present on invading organisms or transplanted tissues interact with the antigen receptor of T lymphocytes to induce a complex series of changes which result in T cell proliferation and the acquisition of immunologic competence. Our objectives over the next five years are to gain insight into the genetic regulatory events which underly T cell activation. Specifically, we hope to understand how events initiated at the antigen receptor are transmitted to the nucleus and result in the activation of a group of genes including those for IL-2, the IL-2 receptor, and gamma interferon. Each of the specific aims of this proposal describes an approach to characterizing the molecules which transmit these signals. We will begin our investigation by characterizing two nuclear proteins, NFIL2A and E, that we have recently discovered which bind to essential sequences within the IL-2 enhancer as well as the HIV LTR. NFIL2E is present only in activated T lymphocytes. It appears within 20 minutes of the binding of antigen to the antigen receptor and precedes IL-2 gene activation by 10-15 minutes. The second protein, NFIL2A, is constitutive but its recognition sequence is able information gained in an initial characterization of these molecules to obtain antibodies and cDNA clones for these proteins. These materials will be used to answer several specific questions including: what is the nature of the antigen-receptor dependent activation of these molecules? how is this process inhibited by cyclosporin? and finally are these proteins transcriptional factors or do they function by another mechanism? Our goal will be to learn how these molecules are involved in T cell activation and T cell proliferation. The last specific aim describes a novel approach to selecting mutations at various levels in the normal pathways of T cell activation. We will prepare transgenic mice using the T-cell specific and activation-specific transcription enhancer of the IL- 2 gene directing transcription stimulus each time the antigen receptor is triggered, but should not escape antigenic control unless a mutation develops in the normal pathways of T cell activation. These mutations in T cell activation will be identified and the site and biologic behavior of the mutations characterized using the reagents derived in Specific Aims 1 and 2.